Acoustic device



w. F. KANN ENBERG 2,226,934

ACOUSTIC DEVICE 'Filed Sept. 24. 1958 FIG. 2

INVENTOR 8y WE/(ANNENBERG ATZORNEY Patented Dec. 31,

ACOUSTIC msvrcn Walter F. Kannenberg, Rutherford, N. J., assignor toBell Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New York Application September 24, 1938, Serial .No.231,487

17 Claims. (Cl. 179-119) This invention relates to acoustic devices andFig. 3 is asectional view taken on line 33 of more particularly toacoustic transmitters of the Fi 1; type commonly referred to as ribbonmicrophones. Fig. 4 is a front elevational view of a ribbon 'Ribbonmicrophones comprise in general, a -microphone illustrative of anotherembodiment a light-weight diaphragm in the form of an elecof thisinvention; v t trically conductive strip or ribbon disposed in a i 5 isa si e ie Pa y n sectidmalon magnetic field of a suitable magneticstructure. e o ig. of the micr ph n W in Vibrations of the ribbon orstrip in accordance and with sound waves impinging therein result in thez- 6 is a onal v w t n along lin 66 generation of correspondingelectromotive forces of I h m in the ribbon and a circuit of which itforms a Referring w to t e d w in the embodir part. ment of theinvention shown in Figs. 1, 2 and 3,

In such microphones, the impedance of the rib- 9 and H (18110139elongated mbers or polebon diaphragm and the circuit of which it formspleces of magnetlc matel'lal mounted in Sp H5 a part is quite low andnecessitates the use of a parallel relation and extending between andtransformer of high step-up ratio for obtaining abutting the Pole-facesof two Permanent a satisfactory matching of the impedance of the netsand of generally horseshoe -U microphone to that of the grid or inputcircuit The members and g 5 are secured at each of an associatedamplifier to which the output to support members M d 55 by i g an of theamplifier is suppliem means such as screws it. The members it and Oneobject of this invention is to facilitate the are of nonfmafgnetic m aand are Prefer attainment of a satisfactory impedance matching ably ofelectncal msulatwn- E of h sPpport between a transmitter such as aribbon micromembers and an Integral PRO-196th phone and the input or,grid circuit of an amplior boss n mterfittmg with one of ihevmagnefis235 fier associated therewith. 12 or IS. The magnets, as shown, areeheldin as Another object of this invention is to improve 3 55 bosfises and gq attracthe structure and performance of ribbon microon mem ers and n Ifother phones fastening means, such as screws, bolts, clamps or Inaccordance with one feature of this inven- 1 also be employed betweenmagnets. tion. a ribbon microphone comprises a magnetic ,ggz ig g and if g g diaphragm vibratile in the field of a magnet th 2 th erye as t 06structure, andcurrent carrying means, such as g 8 en 2;; edmphragmm'whmn y be a coil or coi1s,'associated with the magnet struc- S up r nof Penna W or qther Sultable i magnetic material and preferably 15corrugated a time so that vibrations of the diaphragm produce throughoutthe .major omen of 1 n m variations in the flux linkages of the coil orcoils Permanoy may be define? as an auo 1 i whereby an electromotiveforce is induced therein. nickel to the extent of 30 per cent snore 2phone comprise a g reat numberof turns of ex-- pro-petty of high initialpermeability other matremely fine wire whereby a high impedance temals''suchas moiybdgr-mm' may be added to enabling satisfactory impedancematching with b f m gf ggg it g .-'e eerworemoa mm 11. eri on g1$aiglg1tcircuit of an associated amplifier, 18 may be the order of one quartermil in thick ness nd se ur b a The invention and the foregoing and otherg' f g asses byvscmws and features thereof will be understood moreclearly As shown cleari in E 3 a d fully from the following detaileddescription y the members Gr s pole-pieces l0 and II have inwardly oectin witigihreference to the accompany g drawlng in reduced portions 2|and 22, respectivegi. Elon w c gated output or sound current coils 23and 24 m 1 s a front elevatlonal View of a i b are secured respectivelytothe portions 2| and mic op e illustrative of One-embodiment 0f 22bycement or other suitable means.- Each coil this invention; I e has onelong side on the face of a pole-piece op- 2 is a side view, pa t y insec a o posite the edge of the ribbon l8 and slightly line 2-2 of'Fig.1,, of the ribbon microphone spaced therefrom. 'In other words, thesecoil shown in Fig. 1; portions occupy the portion of the air-gap adableconductor 25 and to terminals, one of which .is shown at 26, byconductors 21 and 28. The

coils preferably comprise a large number of turns, for example, over onethousand, of very fine wire such as No. 44 B and S gauge, or smaller.

The magnets l2 and I3 have like poles in contact with members If! andII, respectively, as indicated by the letters N and S in Fig. l. Thelines of magnetic force in the space between the pole-piece members 2|and 22 are concentratedby the magnetic ribbon l8. v

Sound waves impinging on the diaphragm l8 cause it to vibrate and shiftthe concentrated lines of force relative to the portions of coils 23 and24 in the air-gap. A voltage is induced in each of the many conductorsof the coil portions in accordance with the diaphragm vibrations. Thecoils 23 and 24 are so wound and connected that these voltages areadditive. In 'view of'the high impedance of the coils 23 and 24 theoutput may be fed directly to an amplifier, not shown.

7 in Figs. 4, 5 and 6 is generally similar-to that The embodiment of theinvention illustrated shown in Figs. 1, 2 and 3. Elements of Figs. 4, 5and 6, corresponding to those of Figs. 1, 2, and

3 are designated bythe reference character usedin the latter figures,increased by 30. V

The magnetic corrugated, ribbon diaphragm 48 is mounted between theparallel elongated polepieces 40 and 4| and has its end portions securedto blocks 41 of magnetic material,- as by clamping strips and bolts 48.The blocks 41. may be affixed to the non-magnetic, and preferablyinsulating, support. members ll and 45 by the bolts 49' and provide apath of low reluctance between diaphragm l8 and the the .ends of ,theribbon magnets 42 and 43.

An elongated output or sound current coil 53 has its long sides 54' and55 secured to a face "of each of pole-piece portions BI and 52,respectively,

by cement or other suitable means. Each end of the coil 53 maybe offsetas shown'at 5a in Fig. 5

to prevent interference with the ribbon l8. The coil 53 may be connectedto suitable terminal I means by conductors?! and, which may be integralextensions of the coil,

One such terminal means is shown at 59. Coil 53, as coils 23 and 24,preferably comprises a large number of turns of very fine wire. V

Itwillbe noted that in the embodiment shown in Figs. 4, 5 and 6, ascompared with that of Figs.

1, 2 and 3, but one output coil isprovided and thatthe blocks 41 aroundwhich the magnets are fitted, are of magnetic material.

The magnets 42 and 43' are magnetized with like poles at each end andwith the opposite pole in the middle as indicated by the letters N and Sin Fig. 4. The linesof magneticforce are con-' centrated in the region'occupied bi coil sides 54 and 55 by the magnetic ribbon 48 andthepolepiece portions SI and 52.' Vibrations of the ribbon in response tosound waves generate additive voltages in the two coil portions 54 and55.

It is to be understood thatthe embodiments of the invention shown anddescribed are but illustrative and are-not to be taken as limiting the sp of invention which is defined by. the appended claims only. 1

What is claimed is:

1. An acoustic device comprising a magnetic structure, spacedpole-pieces attached to said, structure, current carrying means having aportion between said pole-pieces, and a ribbon dia- 15 phragm ofmagnetic material also between the pole-pieces;

2. An acoustic device comprising a structure including magnet means,spaced pole-pieces and support means, sound-current coil means having 10elongated portions fixed to said pole-pieces, and a ribbon diaphragm ofmagnetic material attached at its ends to said structure and extendingbetween and in the same direction as the elongated coil portions. .15

3. An acoustic device comprising a magnetic structure havingpole-pieces, said pole-pieces having planar, parallel surfaces, coilmeans havin portions adjacent said surfaces, and a ribbon diaphragm ofmagnetic material extending between 20 said coil portions.

4. An acoustic transmitter comprising a pair of spaced parallelpole-pieces, magnetic means coupled to said pole-pieces, currentcarrying means comprising turns of fine wire and having 25 portionsthereof fixed to said pole-pieces and located therebetween, and a ribbondiaphragm of magnetic material mounted between the coil portions. A

5. An acoustic transmitter comprising a magnetic structure having spacedparallel pole-pieces, a ribbon diaphragm of magnetic material mountedbetween said pole-pieces, and coil means having portions thereof fixedto said pole-pieces adjacent the diaphragm, said coil means comprisingat least one thousand turns of wire having a cross-sectional area ofless than four circular 6. Magnetic circuit means for an acoustictransmitter comprising magnet means, and a ribbon diaphragm of permalloyabout 0.25 mil in thickness in cooperative relation with said pole-piecemeans.

7. An acoustic transmitter comprising a magnetic structure, voice coilmeans, and a ribbon diaphragm of molybdenum permalloy mounted inoperative relation to said structure and *coil means.

8. An acoustic transmitter .comprising spaced parallel pole-piecesdefining an air-gap, permanent magnets, connecting means of non-conducting, non-magnetic material attached to ends of the pole-pieces an'dpositioning the magnets in contact with said ends, current coils one oneach pole-piece and each having a "portion thereof fixed on the air-gapbounding. face of a pole-piece, and magnetic field distorting meanscomprising a sound responsive ribbon of magnetic material attached atits endsto the connecting means and 50 positioned in the air-gap betweensaid portions of said coils.

9. An acoustic transmitter comprising a mag netic structure havingspaced parallel pole-pieces,

coil means having portions thereof attached to 65 r th pole-pieces, anda ribbon diaphragm of ma netic material magnetically in circuit withsaid magnetic structure and mounted for vibration between saidpole-pieces.

' pieces to define a magnetic circuit network in- 15 eans, pole-piececluding elongated air-gaps, and coil means having portions thereof insaid air-gaps, said portions being fixed to the pole-pieces.

11. An acoustic transmitter comprising a magnetic structure havingspaced parallel pole-pieces, a ribbon diaphragm of molybdenum permalloyattached to the magnetic structure, extending between and parallel tothe pole-pieces, and a pair of coils attached to the magnetic structureone on either side of the ribbon, and each having a portion thereoflocated between the ribbon and the magnetic structure. I

12. An acoustic transmitter comprising a magnetic structure havingspaced parallel pole-pieces, coil means having spaced portions thereofbetween and attached to the pole-pieces, and a diaphragm comprising athin ribbon ct permalloy attached at each end to the magnetic structureand located in the space between said coil portions.

13. An acoustic transmitter comprising a pair of permanent magnetsmounted in spaced relation and having a pair of spaced parallelpolepieces therebetween, an elongated coil having spaced parallel sides,one fixed on each pole-piece, and a ribbon diaphragm of magneticmaterial mounted between the parallel sides of the coil.

14. An acoustic transmitter comprising a pair of spaced parallelpole-pieces, magnet means at tached to said pole-pieces, a'ribbondiaphragm of magnetic material between said pole-pieces and magneticallyconnected to the magnet means, and

a voice coil having portions thereof fixed to each pole-piece adjacentto, but spaced from the diaphragm, said magnet means being so poled thatthe pole-pieces are each oi the same magnetic polarity.

15. An acoustic device comprising a pair of magnets having poles ofopposite polarity, a pair .of magnetic members magnetically connectinglike poles of said magnets, a magnetic diaphragm between said magneticmembers, and a coil having a portion in the magnetic field between saiddiaphragm and one or said magnetic members.

16. An acoustic device comprising a pair of magnets having end portionsof like polarity, magnetic members connecting corresponding ends of saidmagnets, a magnetic diaphragm betweensaid magnetic members, magneticmeans'coupling spaced portions of said'diaphragm to said magnets, and acoil having a portion between said 20

